Regarding DropDownList

Question

I have 4 dropdownlist with autopostback="true" to retrive data on SelectedIndexChanged, so i added select as first value in ddl like
<asp:DropDownList ID="ddl3" runat="server" AppendDataBoundItems="true" AutoPostBack="true" onselectedindexchanged="ddl3_SelectedIndexChanged">
                    <asp:ListItem>Select</asp:ListItem>
                </asp:DropDownList>

but when i go from 1st ddl to 2nd ddl the selected value in 1st ddl remains same but i want it come on select value how can i do that
also after page refresh all ddl value must come on select.
Thank You